diff --git a/src/importdxf.cpp b/src/importdxf.cpp
index 2db8836f..f5c44086 100644
--- a/src/importdxf.cpp
+++ b/src/importdxf.cpp
@@ -1068,8 +1068,9 @@ public:
     }
 };
 
-static void ImportDwgDxf(const Platform::Path &filename,
-                         std::function<bool(const std::string &data, DRW_Interface *intf)> read) {
+static void
+ImportDwgDxf(const Platform::Path &filename,
+             const std::function<bool(const std::string &data, DRW_Interface *intf)> &read) {
     std::string fileType = ToUpper(filename.Extension());
 
     std::string data;
diff --git a/src/lib.cpp b/src/lib.cpp
index 052768d2..c16206b1 100644
--- a/src/lib.cpp
+++ b/src/lib.cpp
@@ -13,7 +13,7 @@ static System SYS;
 
 static int IsInit = 0;
 
-void SolveSpace::Platform::FatalError(std::string message) {
+void SolveSpace::Platform::FatalError(const std::string &message) {
     fprintf(stderr, "%s", message.c_str());
     abort();
 }
diff --git a/src/platform/gui.h b/src/platform/gui.h
index 50bebc3e..c5d082c1 100644
--- a/src/platform/gui.h
+++ b/src/platform/gui.h
@@ -102,7 +102,7 @@ std::string AcceleratorDescription(const KeyboardEvent &accel);
 #if defined(__GNUC__)
 __attribute__((noreturn))
 #endif
-void FatalError(std::string message);
+void FatalError(const std::string &message);
 
 // A native settings store.
 class Settings {
diff --git a/src/platform/guigtk.cpp b/src/platform/guigtk.cpp
index 61181482..73fb01ec 100644
--- a/src/platform/guigtk.cpp
+++ b/src/platform/guigtk.cpp
@@ -50,7 +50,7 @@ static std::string PrepareMnemonics(std::string label) {
     return label;
 }
 
-static std::string PrepareTitle(std::string title) {
+static std::string PrepareTitle(const std::string &title) {
     return title + " — SolveSpace";
 }
 
@@ -58,7 +58,7 @@ static std::string PrepareTitle(std::string title) {
 // Fatal errors
 //-----------------------------------------------------------------------------
 
-void FatalError(std::string message) {
+void FatalError(const std::string &message) {
     fprintf(stderr, "%s", message.c_str());
     abort();
 }
diff --git a/src/platform/guimac.mm b/src/platform/guimac.mm
index 3d9108b4..0a1078df 100644
--- a/src/platform/guimac.mm
+++ b/src/platform/guimac.mm
@@ -84,7 +84,7 @@ crash_info_t crashAnnotation __attribute__((section("__DATA,__crash_info"))) = {
     CRASH_VERSION, NULL, NULL, NULL, NULL, NULL, NULL
 };
 
-void FatalError(std::string message) {
+void FatalError(const std::string &message) {
     crashAnnotation.message = message.c_str();
     abort();
 }
diff --git a/src/platform/guinone.cpp b/src/platform/guinone.cpp
index 31f37dcd..85beae37 100644
--- a/src/platform/guinone.cpp
+++ b/src/platform/guinone.cpp
@@ -22,7 +22,7 @@ namespace Platform {
 // Fatal errors
 //-----------------------------------------------------------------------------
 
-void FatalError(std::string message) {
+void FatalError(const std::string &message) {
     fprintf(stderr, "%s", message.c_str());
 
 #if !defined(LIBRARY) && defined(HAVE_BACKTRACE)
diff --git a/src/platform/guiwin.cpp b/src/platform/guiwin.cpp
index 40f20c51..b2ae8105 100644
--- a/src/platform/guiwin.cpp
+++ b/src/platform/guiwin.cpp
@@ -152,13 +152,12 @@ static int Clamp(int x, int a, int b) {
 
 bool handlingFatalError = false;
 
-void FatalError(std::string message) {
+void FatalError(const std::string &message) {
     // Indicate that we're handling a fatal error, to avoid re-entering application code
     // and potentially crashing even harder.
     handlingFatalError = true;
 
-    message += "\nGenerate debug report?";
-    switch(MessageBoxW(NULL, Platform::Widen(message).c_str(),
+    switch(MessageBoxW(NULL, Platform::Widen(message + "\nGenerate debug report?").c_str(),
                        L"Fatal error — SolveSpace",
                        MB_ICONERROR|MB_TASKMODAL|MB_SETFOREGROUND|MB_TOPMOST|
                        MB_OKCANCEL|MB_DEFBUTTON2)) {
diff --git a/src/polygon.h b/src/polygon.h
index b7c5a71e..a9a754c4 100644
--- a/src/polygon.h
+++ b/src/polygon.h
@@ -403,11 +403,10 @@ public:
 
     Vertex *AddVertex(const Vector &pos);
     Edge *AddEdge(const Vector &p0, const Vector &p1, uint32_t kind, uintptr_t data = 0);
-    void Generate(
-        std::function<void(Vertex *start, Vertex *next, Edge *edge)> startFunc,
-        std::function<void(Vertex *next, Edge *edge)> nextFunc,
-        std::function<void(Edge *)> aloneFunc,
-        std::function<void()> endFunc = [](){});
+    void Generate(std::function<void(Vertex *start, Vertex *next, Edge *edge)> const &startFunc,
+                  std::function<void(Vertex *next, Edge *edge)> const &nextFunc,
+                  std::function<void(Edge *)> const &aloneFunc,
+                  std::function<void()> const &endFunc = []() {});
 
     void MakeFromEdges(const SEdgeList &sel);
     void MakeFromOutlines(const SOutlineList &sol);
diff --git a/src/polyline.cpp b/src/polyline.cpp
index bddf1ab7..64aef4e9 100644
--- a/src/polyline.cpp
+++ b/src/polyline.cpp
@@ -141,10 +141,9 @@ PolylineBuilder::Edge *PolylineBuilder::AddEdge(const Vector &p0, const Vector &
 }
 
 void PolylineBuilder::Generate(
-        std::function<void(Vertex *start, Vertex *next, Edge *edge)> startFunc,
-        std::function<void(Vertex *next, Edge *edge)> nextFunc,
-        std::function<void(Edge *alone)> aloneFunc,
-        std::function<void()> endFunc) {
+    std::function<void(Vertex *start, Vertex *next, Edge *edge)> const &startFunc,
+    std::function<void(Vertex *next, Edge *edge)> const &nextFunc,
+    std::function<void(Edge *alone)> const &aloneFunc, std::function<void()> const &endFunc) {
     bool found;
     bool loop = false;
     do {
diff --git a/src/render/gl3shader.cpp b/src/render/gl3shader.cpp
index 542eb97f..888779d3 100644
--- a/src/render/gl3shader.cpp
+++ b/src/render/gl3shader.cpp
@@ -162,7 +162,7 @@ void Shader::Clear() {
     glDeleteProgram(program);
 }
 
-void Shader::SetUniformMatrix(const char *name, double *md) {
+void Shader::SetUniformMatrix(const char *name, const double *md) {
     Enable();
     float mf[16];
     for(int i = 0; i < 16; i++) mf[i] = (float)md[i];
@@ -621,11 +621,11 @@ void EdgeRenderer::Draw(const SEdgeList &edges) {
     Remove(handle);
 }
 
-void EdgeRenderer::SetModelview(double *matrix) {
+void EdgeRenderer::SetModelview(const double *matrix) {
     shader.SetUniformMatrix("modelview", matrix);
 }
 
-void EdgeRenderer::SetProjection(double *matrix) {
+void EdgeRenderer::SetProjection(const double *matrix) {
     shader.SetUniformMatrix("projection", matrix);
 }
 
@@ -833,11 +833,11 @@ void OutlineRenderer::Draw(const SOutlineList &outlines, Canvas::DrawOutlinesAs
     Remove(handle);
 }
 
-void OutlineRenderer::SetModelview(double *matrix) {
+void OutlineRenderer::SetModelview(const double *matrix) {
     shader.SetUniformMatrix("modelview", matrix);
 }
 
-void OutlineRenderer::SetProjection(double *matrix) {
+void OutlineRenderer::SetProjection(const double *matrix) {
     shader.SetUniformMatrix("projection", matrix);
 }
 
@@ -1037,14 +1037,14 @@ bool IndexedMeshRenderer::NeedsTexture() const {
         selectedShader == &pointShader;
 }
 
-void IndexedMeshRenderer::SetModelview(double *matrix) {
+void IndexedMeshRenderer::SetModelview(const double *matrix) {
     colShader.SetUniformMatrix("modelview", matrix);
     texShader.SetUniformMatrix("modelview", matrix);
     texaShader.SetUniformMatrix("modelview", matrix);
     pointShader.SetUniformMatrix("modelview", matrix);
 }
 
-void IndexedMeshRenderer::SetProjection(double *matrix) {
+void IndexedMeshRenderer::SetProjection(const double *matrix) {
     colShader.SetUniformMatrix("projection", matrix);
     texShader.SetUniformMatrix("projection", matrix);
     texaShader.SetUniformMatrix("projection", matrix);
diff --git a/src/render/gl3shader.h b/src/render/gl3shader.h
index ae5ed33d..1831e792 100644
--- a/src/render/gl3shader.h
+++ b/src/render/gl3shader.h
@@ -74,7 +74,7 @@ public:
               const std::vector<std::pair<GLuint, std::string>> &locations = {});
     void Clear();
 
-    void SetUniformMatrix(const char *name, double *md);
+    void SetUniformMatrix(const char *name, const double *md);
     void SetUniformVector(const char *name, const Vector &v);
     void SetUniformVector(const char *name, const Vector4f &v);
     void SetUniformColor(const char *name, RgbaColor c);
@@ -163,8 +163,8 @@ public:
     void Draw(const Handle &handle);
     void Draw(const SEdgeList &edges);
 
-    void SetModelview(double *matrix);
-    void SetProjection(double *matrix);
+    void SetModelview(const double *matrix);
+    void SetProjection(const double *matrix);
     void SetStroke(const Canvas::Stroke &stroke, double pixel);
 };
 
@@ -203,8 +203,8 @@ public:
     void Draw(const Handle &handle, Canvas::DrawOutlinesAs mode);
     void Draw(const SOutlineList &outlines, Canvas::DrawOutlinesAs mode);
 
-    void SetModelview(double *matrix);
-    void SetProjection(double *matrix);
+    void SetModelview(const double *matrix);
+    void SetProjection(const double *matrix);
     void SetStroke(const Canvas::Stroke &stroke, double pixel);
 };
 
@@ -252,8 +252,8 @@ public:
     void Draw(const Handle &handle);
     void Draw(const SIndexedMesh &mesh);
 
-    void SetModelview(double *matrix);
-    void SetProjection(double *matrix);
+    void SetModelview(const double *matrix);
+    void SetProjection(const double *matrix);
 
     bool NeedsTexture() const;
 
diff --git a/src/render/render.cpp b/src/render/render.cpp
index 3ef7171b..ca2a26eb 100644
--- a/src/render/render.cpp
+++ b/src/render/render.cpp
@@ -444,12 +444,11 @@ void ObjectPicker::DrawPixmap(std::shared_ptr<const Pixmap> pm,
     DrawQuad(o, o.Plus(u), o.Plus(u).Plus(v), o.Plus(v), hcf);
 }
 
-bool ObjectPicker::Pick(std::function<void()> drawFn) {
+bool ObjectPicker::Pick(const std::function<void()> &drawFn) {
     minDistance = VERY_POSITIVE;
     maxZIndex = INT_MIN;
 
     drawFn();
     return minDistance < selRadius;
 }
-
 }
diff --git a/src/render/render.h b/src/render/render.h
index 825ca8d1..649256e7 100644
--- a/src/render/render.h
+++ b/src/render/render.h
@@ -261,7 +261,7 @@ public:
     void DoQuad(const Vector &a, const Vector &b, const Vector &c, const Vector &d,
                 int zIndex, int comparePosition = 0);
 
-    bool Pick(std::function<void()> drawFn);
+    bool Pick(const std::function<void()> &drawFn);
 };
 
 // A canvas that renders onto a 2d surface, performing z-index sorting, occlusion testing, etc,
diff --git a/src/resource.cpp b/src/resource.cpp
index 6e9ce727..7b19081e 100644
--- a/src/resource.cpp
+++ b/src/resource.cpp
@@ -918,7 +918,7 @@ Vector VectorFont::GetExtents(double forCapHeight, const std::string &str) {
 }
 
 void VectorFont::Trace(double forCapHeight, Vector o, Vector u, Vector v, const std::string &str,
-                       std::function<void(Vector, Vector)> traceEdge) {
+                       const std::function<void(Vector, Vector)> &traceEdge) {
     ssassert(!IsEmpty(), "Expected a loaded font");
 
     double scale = (forCapHeight / capHeight);
@@ -945,7 +945,7 @@ void VectorFont::Trace(double forCapHeight, Vector o, Vector u, Vector v, const
 }
 
 void VectorFont::Trace(double forCapHeight, Vector o, Vector u, Vector v, const std::string &str,
-                       std::function<void(Vector, Vector)> traceEdge, const Camera &camera) {
+                       const std::function<void(Vector, Vector)> &traceEdge, const Camera &camera) {
     ssassert(!IsEmpty(), "Expected a loaded font");
 
     // Perform grid-fitting only when the text is parallel to the view plane.
diff --git a/src/resource.h b/src/resource.h
index 6c14dad8..bb0e1c7a 100644
--- a/src/resource.h
+++ b/src/resource.h
@@ -103,9 +103,9 @@ public:
     Vector GetExtents(double forCapHeight, const std::string &str);
 
     void Trace(double forCapHeight, Vector o, Vector u, Vector v, const std::string &str,
-               std::function<void(Vector, Vector)> traceEdge);
+               const std::function<void(Vector, Vector)> &traceEdge);
     void Trace(double forCapHeight, Vector o, Vector u, Vector v, const std::string &str,
-               std::function<void(Vector, Vector)> traceEdge, const Camera &camera);
+               const std::function<void(Vector, Vector)> &traceEdge, const Camera &camera);
 };
 
 #endif